Migration

---

What to Use to Know When to Go?

Light levels
Temperature
Food availability
Physiological changes
Endogenous clocks (circannual and circadian)

Advantages?
Disadvantages?

How to Know Where to Go?

Learned
Innate
Combination

---

Go the Distance

Time

• Interruptions?
• Irregular flight speed?

Metabolic energy consumption

• Irregular flight speed?

Optic flow

Landmarks

• First flight?

---

Photoperiod and Circannual Clock

Accelerate by short and long photoperiods
Birth time/age
Distance to travel
Species differences

• Ranges

---

Where to Go the First Time?

Learned

• Social

Genetic

• Social and non-social
• Developmental changes
  • Innate: 'vector orientation'
  • Learned: 'site imprinting'
• Different populations, different vectors
  

• Mix different gene groups...
  • ...intermediate vector orientation
• Black caps
  • One or few loci control vector orientation
  • Rapid evolution

---

Features of Innate Vector Orientation

1. Geomagnetic field
2. Axis of celestial rotation

• Modifies (1) through interaction
  

Night: star rotation
• Day: sun's path or polarized light patterns

---

Energy Constraints

To refuel...

• Barriers
• Time
• Risk (e.g., predation)
• New habbitat

...or not to refuel...?

• Time
• Energy (weight:cost)

Bird morphology and fuel load

• Soaring or flapping

---

Considerations for Migrating Birds

Open circles: energy/water constraint; Squares: navigational considerations; Triangle: correct seasonal timing

Considerations for Migrating Mammals

Can you think of some ways that the considerations of migration might be different for terrestrial mammals than for birds?